Fatigue Behavior of Spot Welds under Variable-Amplitude Loading

This paper presents data and methods for predicting fatigue lives of spot welds subjected to variable amplitude random-sequence load fluctuations. An equivalence between the fatigue behavior of spot welds under constant amplitude and under variable-amplitude cyclic-load fluctuations is also established by using an effective damage-parameter range approach. The analyses presented show that the damage parameter for fatigue of spot welds is $\Delta E = \Delta P\sqrt {\Delta {\theta _N}} /t$ where ΔP and ΔθN are the fluctuations in the applied stress and in the nugget rotation respectively. The analyses also show that the effective damage-parameter range derived by using the Miner cumulative damage law, EMiner, resulted in an excellent correlation of fatigue lives for spot welds under variable-amplitude and constant-amplitude cyclic loading. The root-meansquare, RMS, damage-parameter range, resulted in a conservative correlation.